Increased popularity and use of the communication networks have made possible new methods of doing business, marketing goods and providing services to consumers or users. To insure that sensitive information, such as business strategy, credit card numbers, social security numbers, bank account balances, medical records, etc., are not disclosed when transmitted over unsecured networks, sensitive data items are encrypted (or encoded). Methods of encrypting sensitive information are well known in the art. For example, in a secure communication network, one party may possess an encoding key that is used to encrypt sensitive data items, while the receiving party possess a corresponding decrypting key to return a received encrypted message to its original form. In this method, if the encoding or decoding key becomes known to parties outside the secure network, the entire system is compromised as unauthorized parties are also able to decrypt encoded messages. To prevent unauthorized access to sensitive information, encoding and decoding keys are continuously changed. However, continuously changing encoding and decoding keys is burdensome as it requires the redistribution of new keys to each authorized member. However, during the distribution process, communication among the parties is limited until the new keys are distributed to all authorized members.
Another method of encryption that reduces the burden of redistributing encoding/decoding keys is the use of a public-and-private key system. As is known, a public-and-private key system, a first party issues a non-secret public key, over a communication network, such as a the public telephone system (PSTN), private telephone system, Internet, etc., while retaining, secretly, a private key. The public key is accessible to all parties that have access to the network, while access to the private key is limited solely to the issuing party. Members of the secure communication network can then use a received public key and their own retained private key to generate an encryption key that can be used to encrypt sensitive informational data items. The encrypted sensitive informational data message, when received by the party issuing the public key, can then be decrypted using an encryption key generated from a previously received public key and the retained private key. Thus, sensitive information messages can be securely transmitted between parties without the necessity of transferring secure keys by other methods or coordinating the use of previously transferred secure keys. Public-and-private key systems are well known in the art. Details of their operation are disclosed in U.S. Pat. No. 4,200,770, entitled “Cryptographic Apparatus and Method,” dated Apr. 29, 1980, to Hellmman, et al., and U.S. Pat. No. 4,405,829, entitled “Cryptographic Communication System and Method,” dated, Sep. 20, 1983, to Rivest, et al.
However, the public-and-private key systems are subject to unauthorized access also. Public-and private key systems transmit public key parameters without the benefit of any security protection over unsecured networks. Hence, these initial parameters can be intercepted and used to attack the encryption key. Methods of attacking encryption keys, e.g., complex reverse mathematical algorithms, “brute force,” etc., are also well known in the art and need not be discussed in detail herein. In these methods, the amount of encrypted data intercepted increases the chance of successfully determining the underlining encryption key. Consequently, a substantially long message may be successfully attacked and the security benefit of the encryption key can be lost.
One method to prevent the transmission of long messages using a single encryption key is to simply change the key during transmission. However, while the transmitting party may change the encryption key dynamically, the receiving party must be informed of the changed encryption key in order to decrypt subsequent messages. This places a burden on the parties as an indicator of a new key must be sent before the transmission. Hence, there is a need to dynamically change encryption keys during the transmission of substantially long messages and to provide the receiving party with knowledge of the encryption key used for the transmission without imposing burdens on the parties.